Method for producing a high-strength steel strip with improved properties for further processing, and a steel strip of this type

ABSTRACT

A steel strip is produced by melting a steel melt containing (In wt. %): C: 0.1 to &lt;0.3; Mn: 4 to &lt;8; Al: &gt;1 to 2.9; P: &lt;0.05; S: &lt;0.05; N: &lt;0.02; remainder iron including unavoidable steel-associated elements. The steel melt is cast to form a pre-strip or to form a slab and heated to a rolling temperature of 1050 to 1250° C. or in-line rolling out of the casting heat. The pres-strip or slab is hot rolled into a hot strip having a thickness of 12 to 0.8 mm, at a final rolling temperature of 1050 to 800° C. The hot strip is reeled at a temperature of more than 200 to 800° C., pickled, annealed for an annealing time of 1 min to 48 h and at a temperature of 540 to 840° C., and cold rolled at room temperature or elevated temperature in at least one rolling pass.

The invention relates to a method for producing an ultra high strengthsteel strip with improved properties during further processing, and to acorresponding steel strip.

In particular, the invention relates to the production of a steel stripconsisting of a manganese-containing TRIP (Transformation InducedPlasticity) and/or TWIP (Twinning Induced Plasticity) steel havingexcellent cold-formability and warm-formability, increased resistance tohydrogen-induced delayed crack formation (delayed fracture), to hydrogenembrittlement and to liquid metal embrittlement during welding.

European patent application EP 2 383 353 A2 discloses amanganese-containing steel, a flat steel product formed from this steeland a method for producing this flat steel product. The steel has atensile strength of 900 to 1500 MPa and an elongation at fracture A80 ofat least 4%. The highest described elongation at fracture A80 is 8%.Furthermore, the steel consists of the elements (contents are in weightpercent and relate to the steel melt): C: to 0.5; Mn: 4 to 12.0; Si: upto 1.0; Al: up to 3.0; Cr: 0.1 to 4.0; Cu: up to 4.0; Ni: up to 2.0; N:up to 0.05; P: up to 0.05; S: up to 0.01, with the remainder being ironand unavoidable impurities. Optionally, one or more elements from thegroup “V, Nb, Ti” are provided, wherein the sum of the contents of theseelements is at most equal to 0.5. For an Mn content of 5 and an Alcontent of 2, the total is 7. The microstructure of this flat steelproduct consists of 30 to 100% martensite, tempered martensite orbainite, with the remainder being austenite. This steel is said to becharacterised in that it can be produced in a more cost-effective mannerthan steels containing a high content of manganese and at the same timehas high elongation at fracture values and, associated therewith, aconsiderably improved deformability. A method for producing a flat steelproduct from the high-strength, manganese-containing steel describedabove comprises the following working steps: —melting the previouslydescribed steel melt, —producing a starting product for subsequent hotrolling, in that the steel melt is cast into a string, from which atleast one slab or thin slab is separated off as a starting product forthe hot rolling, or into a cast strip which is supplied to the hotrolling process as a starting product, —heat-treating the startingproduct in order to bring the starting product to a hot-rolling startingtemperature of 1150 to 1000° C., —hot rolling the starting product toform a hot strip having a thickness of at most 2.5 mm, wherein the hotrolling is terminated at a hot-rolling end temperature of 1050 to 800°C., —reeling the hot strip to form a coil at a reeling temperature of s700° C. Optionally, the hot strip can be annealed at 250 to 950° C.,subsequently cold-rolled and then annealed at 450 to 950° C. Also,following on from the cold rolling or hot rolling of the flat steelproduct, said product is provided with a metallic corrosion-protectioncoat or an organic coat.

Furthermore, German laid-open document DE 10 2012 013 113 A1 alreadydescribes so-called TRIP steels which have a predominantly ferriticbasic microstructure having incorporated residual austenite which canconvert into martensite during deformation (TRIP effect). The manganesecontent of the steel strip is 1.00 to 2.25 weight percent. The steelstrip is coated and temper-rolled in a melting bath. Owing to itsintense cold-hardening, the TRIP steel achieves high values for uniformelongation and tensile strength. TRIP steels are used inter alia instructural components, chassis components and crash-relevant componentsof vehicles, as sheet metal blanks and as welded blanks.

European patent EP 1 067 203 B1 discloses a method for producing a steelstrip. In this case, a thin strip having a thickness of 1.5 mm to 10 mmis cast from a steel melt consisting at least of the following elements(contents in weight percent) C: 0.001 to 1.6; Mn: 6 to 30; Al: to 6; P:to 0.2; S: to 0.5; N: to 0.3 and the remainder being iron andunavoidable impurities. The thin strip is hot-rolled with a reductiondegree between 10% and 60%, acid-cleaned, cold-rolled with a reductiondegree between 10% and 90% and recrystallisation-annealed for 1 to 2 minat 800 to 850° C.

Japanese patent JP 3 317 303 B2 discloses a high strength steel striphaving the following composition in weight percent: C: 0.05-0.3 Si:<0.2, Mn: 0.5-4.0 P: ≤0.1; S: ≤0.1; Ni: 0-5.0; Al: 0.1-2.0 and N≤0.01.In this case, the following equations are satisfied: Si+Al=0.5; Mn+⅓Ni≥1.0. The microstructure contains ≥5 vol. % residual austenite. In avacuum laboratory furnace, a melt of the previously described steel ismelted. By means of hot-forging, a test block having a thickness of 25mm is produced. This is then heated to 1250° C. in an electric furnacefor one hour. Subsequently, hot rolling is performed at 930 to 1150° C.in order to achieve a steel strip thickness of 5 mm. For reelingsimulation, the steel strip is cooled immediately to 500° C. and isannealed in an electric furnace at this temperature for one hour.

Proceeding from this, the object of the present invention is to providea method for producing an ultra high strength steel strip consisting ofa manganese-containing TRIP and/or TWIP steel having strengths between1100 and 2200 MPa, which is cost-effective and wherein the steel striphas improved properties during further processing, in particular a goodcombination of strength and forming properties, increased resistance tohydrogen-induced delayed crack formation, to hydrogen embrittlement andto liquid metal embrittlement. Furthermore, an ultra high strength andcost-effective steel strip is to be provided having improved propertiesduring further processing.

This object is achieved by a method for producing a flat steel product,in particular using the aforementioned steel, having the features ofclaim 1 and by an ultra high strength steel strip having the features ofclaim 10. Advantageous embodiments of the invention are described in thedependent claims.

In accordance with the invention, a method for producing an ultra highstrength steel strip, comprising the steps of: —melting a steel meltcontaining (in wt. %): C: 0.1 to <0.3; Mn: 4 to <8; Al: >1 to 2.9; P:<0.05; S: <0.05; N: <0.02; with the remainder being iron includingunavoidable steel-associated elements, with optional adding by alloyingof one or more of the following elements (in wt. %): Si: 0.05 to 0.7;Cr: 0.1 to 3; Mo: 0.01 to 0.9; Ti: 0.005 to 0.3; B: 0.0005 to 0.01 viathe process route of blast furnace-steel plant or the electric arcfurnace process each with optional vacuum treatment of the melt;—casting the steel melt to form a pre-strip by means of a horizontal orvertical strip casting process approximating the final dimensions orcasting the steel melt to form a slab or thin slab by means of ahorizontal or vertical slab or thin slab casting process, —heating to arolling temperature of 1050 to 1250° C. or in-line rolling out of thecasting heat, —hot rolling the pre-strip or the slab or the thin slab toform a hot strip having a thickness of 12 to 0.8 mm, at a final rollingtemperature of 1050 to 800° C., —reeling the hot strip at a temperatureof more than 200 to 800° C., —pickling the hot strip, —annealing the hotstrip in a continuous or discontinuous annealing installation for anannealing time of 1 min to 48 h and at temperatures of 540° C. to 840°C., —cold rolling the hot strip at room temperature or elevatedtemperature in one or a plurality of rolling passes, —optionallyelectrolytically galvanising or hot-dip galvanising the steel strip,provides a cost-effectively produced steel strip having a strength of1100 to 2200 MPa, a good combination of strength, elongation and formingproperties and an increased resistance to delayed crack formation, tohydrogen embrittlement and to liquid metal embrittlement, whichadditionally has a TRIP and/or TWIP effect during mechanical loading.

Typical thickness ranges for the pre-strip are 1 mm to 35 mm and forslabs and thin slabs they are 35 mm to 450 mm. Provision is preferablymade that the slab or thin slab is hot-rolled to form a hot strip havinga thickness of 12 mm to 0.8 mm or the pre-strip, cast to approximatelythe final dimensions, is hot-rolled to form a hot strip having athickness of 8 mm to 0.8 mm. The cold strip in accordance with theinvention has a thickness of at most 3 mm, preferably 0.1 to 1.4 mm.

In the context of the above method in accordance with the invention, apre-strip produced with the two-roller casting process and approximatingthe final dimensions and having a thickness of less than or equal to 3mm, preferably 1 mm to 3 mm is already understood to be a hot strip. Thepre-strip thus produced as a hot strip does not have a 100% caststructure owing to the introduced deformation of the two rollers runningin opposite directions. Hot rolling thus already takes place in-lineduring the two-roller casting process which means that separate heatingand hot rolling is not necessary.

The cold rolling of the hot strip can take place at room temperature oradvantageously at elevated temperature prior to the first rolling passin one or a plurality of rolling passes.

The cold rolling at elevated temperature is advantageous in order toreduce the rolling forces and to aid the formation of deformation twins(TWIP effect). Advantageous temperatures of the material being rolledprior to the first rolling pass are 60 to 450° C.

If the cold rolling is performed in a plurality of rolling passes, it isadvantageous to intermediately heat or cool down the steel strip betweenthe rolling passes to a temperature of 60 to 450° C. because the TWIPeffect is brought to bear in a particularly advantageous manner in thisregion. Depending upon the rolling speed and degree of deformation,intermediate heating, e.g. at very low degrees of deformation androlling speeds, and also additional cooling, caused by heating thematerial with rapid rolling and high degrees of deformation, can beperformed.

After cold rolling of the hot strip at room temperature, the steel stripis to be advantageously annealed in particular in a continuous annealinginstallation, advantageously for an annealing time of 1 to 15 min and attemperatures of 720° C. to 840° C., in order to restore sufficientforming properties. Optionally, annealing can be performed by means of adiscontinuous annealing installation at a temperature of 550° C. to 820°C. and an annealing time of 30 min to 48 h. If required in order toachieve specific material properties, this annealing procedure can alsobe performed with the steel strip rolled at elevated temperature.

After the annealing treatment, the steel strip is advantageously cooledto a temperature of 250° C. to room temperature and subsequently, ifrequired, in order to adjust the required mechanical properties, in thecourse of ageing treatment, is reheated to a temperature of 300 to 450°C., is maintained at this temperature for up to 5 min and subsequentlyis cooled to room temperature. The ageing treatment can be performedadvantageously in a continuous annealing installation.

If required, the steel strip can be temper-rolled after the coldrolling, as a result of which the surface structure required for thefinal application is adjusted. The temper rolling can be performed e.g.by means of the Pretex®-method.

In one advantageous development, the steel strip produced in this manneracquires a further coating on an organic or inorganic basis instead ofor after the electrolytic galvanising or hot-dip galvanising. They canbe e.g. organic coatings, synthetic material coatings or lacquers orother inorganic coatings, such as e.g. iron oxide layers.

The steel strip produced in accordance with the invention can be usedboth as a metal sheet, metal sheet portion or blank or can be furtherprocessed to form a longitudinal or helical seam-welded pipe.

Furthermore, the steel sheet or steel strip is suitable in aparticularly advantageous manner for further processing to form acomponent by means of cold forming or warm forming, e.g. In theautomotive industry, in infrastructure construction and engineering.

The steel strip having improved properties during further processing hasa TRIP/TWIP effect, having a microstructure (in vol. %) consisting of 10to 80% austenite, 10 to 90% martensite, with the remaining being ferriteand bainite having a proportion together of less than 20%. In this case,a proportion of at least 20% of the martensite is present as annealedmartensite and optionally a proportion of >10% of the austenite ispresent in the form of annealing or deformation twins.

By reason of the annealing treatments in accordance with the invention,the steel strip has a particularly fine grain with an average grain sizeof the phase components:

austenite: less than 500 nm

martensite, ferrite, bainite: less than 650 nm.

By reason of the final annealing of the cold strip which is produced atroom temperature or at elevated temperatures, the austenite is presentin a metastable state and optionally with deformation twins, as a resultof which it converts partially into martensite when a mechanical forceis applied (e.g. forming) per TRIP effect.

The austenite proportion of the steel in accordance with the inventioncan convert partially or completely into martensite when mechanicalstresses are applied (TRIP effect).

The alloy in accordance with the invention, when subjected to acorresponding mechanical load, also has twinning during plasticdeformation (TWIP effect). Owing to the intense cold-hardening inducedby the TRIP and/or TWIP effect, the steel achieves high values in termsof elongation at fracture, in particular uniform elongation, and tensilestrength.

The steel in accordance with the invention can then be formed in aparticularly advantageous manner by means of warm forming at 60 to 450°C. because the austenite stability at these temperatures at leastpartially suppresses conversion of austenite into martensite (TRIPeffect), wherein 50 to 100% of the starting austenite is retained andoptionally converts partially into deformation twins (TWIP effect). Thedeformation twins can convert into martensite at room temperature withfurther energy being expended (TRIP effect, increased energy absorptioncapacity e.g. in the event of a crash). The residual elongation whichhas remained until the component fails is considerably increased duringwarm forming in comparison with cold forming. Furthermore, theprevention of the TRIP effect during warm forming brings about aconsiderable improvement with respect to undesired hydrogen-inducedinfluences (delayed crack formation, hydrogen embrittlement). Also, thewarm forming advantageously serves to raise the 0.2% elasticity limit ofthe formed material, whereby e.g. the sheet thickness could beadvantageously reduced.

The method in accordance with the invention can be used to produce avery cost-effective steel strip having an alloy concept, in which, inaddition to iron, only the elements carbon, manganese and aluminium arerequired. The required annealing treatment can be performedadvantageously by means of continuous annealing, which is considerablymore economical than batch-type annealing.

A steel strip produced according to the method in accordance with theinvention advantageously has an elasticity limit Rp0.2 of 300 to 1550MPa, a tensile strength Rm of 1100 to 2200 MPa and an elongation atfracture A80 of more than 4 to 41%, wherein high strengths tend to beassociated with lower elongations at fracture and vice versa:

Rm of over 1100 to 1200 MPa: Rm×A80≥25000 up to 45000 MPa %

Rm of over 1200 to 1400 MPa: Rm×A80≥20000 up to 42000 MPa %

Rm of over 1400 to 1800 MPa: Rm×A80≥10000 up to 40000 MPa %

Rm of over 1800 MPa: Rm×A80≥7200 up to 20000 MPa %

A test piece body A80 was used for the elongation at fracture tests asper DIN 50 125.

The elongation and toughness properties are advantageously improved bythe onset of the TRIP and/or TWIP effect of the alloy in accordance withthe invention.

The steel strip produced in accordance with the invention offers a goodcombination of strength, elongation and deformation properties.Moreover, the production of this manganese steel in accordance with theinvention having a medium manganese content (medium manganese steel) onthe basis of the alloy elements C, Mn, Al is very cost-effective.

Owing to the increased Al content, the steel has a lower relativedensity compared with other manganese steels alloyed with a small amountof Al and having medium manganese contents. The manganese steel inaccordance with the invention is also characterised by an increasedresistance to delayed crack formation (delayed fracture) and to hydrogenembrittlement and liquid metal embrittlement during welding.

The use of the term “to” in the definitions of the content ranges, suchas e.g. 0.01 to 1 wt. %, means that the limit values—0.01 and 1 in theexample—are also included.

Alloy elements are generally added to the steel in order to influencespecific properties in a targeted manner. An alloy element can therebyinfluence different properties in different steels. The effect andinteraction generally depend greatly upon the quantity, presence offurther alloy elements and the solution state in the material. Thecorrelations are varied and complex. The effect of the alloy elements inthe alloy in accordance with the invention will be discussed in greaterdetail hereinafter. The positive effects of the alloy elements used inaccordance with the invention will be described hereinafter:

Carbon C: is required to form carbides, stabilises the austenite andincreases the strength. Higher contents of C impair the weldingproperties and result in the impairment of the elongation and toughnessproperties, for which reason a maximum content of less than 0.3 wt. % isset. In order to achieve a sufficient strength for the material, aminimum addition of 0.1 wt. % Is required.

Manganese Mn: stabilises the austenite, increases the strength and thetoughness and renders possible a deformation-induced martensiteformation and/or twinning in the alloy in accordance with the invention.Contents of less than 4 wt. % are not sufficient to stabilise theaustenite and thus impair the elongation properties, whereas withcontents of 8 wt. % and more the austenite is stabilised too much and asa result the strength properties, in particular the 0.2% elasticitylimit, are reduced. For the manganese steel in accordance with theinvention having medium manganese contents, a range of 4 to <8 wt. % ispreferred.

Aluminium Al: an Al content of greater than 1 wt. % improves thestrength and elongation properties, decreases the relative density andinfluences the conversion behaviour of the alloy in accordance with theinvention. Contents of Al of more than 2.9 wt. % impair the elongationproperties. Higher Al contents also considerably impair the castingbehaviour in the continuous casting process. This produces increasedoutlay when casting. Al Contents of more than 1 wt. % delay theprecipitation of carbides in the alloy in accordance with the invention.Therefore, a maximum content of 2.9 wt. % and a minimum content of morethan 1 wt. % are set.

Furthermore, for the sum of Mn and Al a minimum content (in wt. %) ofmore than 6.5 and less than 10 should be maintained in order to be ableto ensure the desired conversion behaviour. A content of Mn+Al of 10 wt.% and more impairs the castability, thus reducing output and thusincreasing costs. In the case of contents of Mn+Al of 6.5 wt. % or less,it is not possible to ensure sufficient austenite stability for thedesired conversion behaviour.

Silicon Si: the optional addition of Si in contents of more than 0.05wt. % impedes the diffusion of carbon, reduces the relative density andincreases the strength and elongation properties and toughnessproperties. Furthermore, an improvement in the cold-rollability could beseen by adding Si by alloying. Contents of more than 0.7 wt. % result inembrittlement of the material and negatively influence the hot- andcold-rollability and the coatability e.g. by galvanising. Therefore, amaximum content of 0.7 wt. % and a minimum content of 0.05 wt. % areset.

Chromium Cr: the optional addition of Cr improves the strength andreduces the rate of corrosion, delays the formation of ferrite andperlite and forms carbides. The maximum content is set to 3 wt. % sincehigher contents result in an impairment of the elongation properties. Aminimum Cr content for efficacy is set to 0.1 wt. %.

Molybdenum Mo: The optional addition of Mo acts as a carbide-formingagent, increases the strength and increases the resistance to delayedcrack formation and hydrogen embrittlement. Contents of Mo of more than0.9 wt. % impair the elongation properties, for which reason a maximumcontent of 0.9 wt. % and a minimum content of 0.01 wt. % required forsufficient efficacy are set.

Phosphorus P: is a trace element from iron ore and is dissolved in theiron lattice as a substitution atom. Phosphorous increases the hardnessby means of solid solution hardening and improves the hardenability.However, attempts are generally made to lower the phosphorous content asmuch as possible because inter alia it exhibits a strong tendencytowards segregation owing to its low diffusion rate and greatly reducesthe level of toughness. The attachment of phosphorous to the grainboundaries can cause cracks along the grain boundaries during hotrolling. Moreover, phosphorous increases the transition temperature fromtough to brittle behaviour by up to 300° C. For the aforementionedreasons, the phosphorus content is limited to values of less than 0.05wt. %.

Sulphur S: like phosphorous, is bound as a trace element in the ironore. It is generally not desirable in steel because it exhibits atendency towards extensive segregation and has a greatly embrittlingeffect, whereby the elongation and toughness properties are impaired. Anattempt is therefore made to achieve amounts of sulphur in the meltwhich are as low as possible (e.g. by deep desulphurisation). For theaforementioned reasons, the sulphur content is limited to values of lessthan 0.05 wt. %.

Nitrogen N: is likewise an associated element from steel production. Inthe dissolved state, it improves the strength and toughness propertiesin steels containing a higher content of manganese of greater than orequal to 4 wt. % Mn. Lower Mn-alloyed steels of less than 4 wt. % withfree nitrogen tend to have a strong ageing effect. The nitrogen diffuseseven at low temperatures to dislocations and blocks same. It thusproduces an increase in strength associated with a rapid loss oftoughness. Binding of the nitrogen in the form of nitrides is possiblee.g. by adding aluminium or titanium by alloying, wherein in particularaluminium nitrides have a negative effect upon the forming properties ofthe alloy in accordance with the invention. For the aforementionedreasons, the nitrogen content is limited to less than 0.02 wt. %.

Titanium Ti: acts in a grain-refining manner as a carbide-forming agent,whereby at the same time the strength, toughness and elongationproperties are improved, and reduces the inter-crystalline corrosion. Ticontents of more than 0.3 wt. % impair the elongation properties, forwhich reason a maximum Ti content of 0.3 wt. % Is set. Optionally, aminimum content of 0.005 is set in order to bind nitrogen andadvantageously precipitate Ti.

Boron B: delays the austenite conversion, improves the hot-formingproperties of steels and increases the strength at ambient temperature.It achieves its effect even with very low alloy contents. Contents above0.01 wt. % greatly impair the elongation and toughness properties, forwhich reason the maximum content is set to 0.01 wt. %. Optionally, aminimum content of 0.0005 wt. % is set in order to advantageously usethe strength-increasing effect of boron.

Tests were performed in order to examine the mechanical properties ofsteel strips produced in accordance with the invention and consisting ofan exemplary alloy 1. The alloy 1 contains, in addition to iron andmelting-induced impurities, extracts of the following elements in thestated contents in wt. %:

Alloy C Mn Al Si Alloy 1 0.2 7.0 1.1 0.5

For the purposes of comparison, the steel strips produced from theabove-mentioned alloy 1 were cold-rolled, i.e. at room temperature andtherefore below 50° C., and also rolled in accordance with the inventionat 250° C. The measured rolling forces are given as follows:

Rolling Rolling force [kN] force [kN] Degree of Reduction incumulative - cumulative - at deformation rolling force Alloy coldrolling 250° C. (e = Δd/d0) [%] [%] Alloy 1 147000 52500 45 ca. 64

Cumulative rolling force is understood to be the adding up of therolling forces of the individual passes in order to obtain a comparablemeasure for the expenditure of force. The rolling force was standardisedto a band width of 1000 mm. The degree of deformation e is defined asthe quotient of the change in thickness Δd of the steel strip underinvestigation and the initial thickness d0 of the steel strip underinvestigation. The reduction in rolling force is the calculated decreasein the rolling force at 250° C. compared with the rolling force duringcold rolling.

The elongation at fracture A80 was also determined:

Elongation at fracture Alloy Rp0.2 [MPa] Rm [MPa] A80 [%] Alloy 1 10001250 18 warm-rolled 250° C. Alloy 1 comparison 400 1180 18 betweencold-rolled and annealed (720° C._10 min)

The elongation characteristic values represent the elongation in therolling direction. It is apparent that there is a considerable increasein the elasticity limit whilst the elongation at fracture remains thesame.

What is claimed is: 1.-18. (canceled)
 19. A method for producing anultra high strength steel strip having a TRIP/TWIP effect, comprising:melting a steel melt containing (in wt. %): C: 0.1 to <0.3; Mn: 4 to <8;Al: >1 to 2.9; P: <0.05; S: <0.05; N: <0.02; with the remainder beingiron including unavoidable steel-associated elements, in a blast furnaceprocess or electric are furnace process; casting the steel melt to forma pre-strip by a horizontal or vertical strip casting processapproximating a final dimension or casting the steel melt to form a slabor thin slab by a horizontal or vertical slab or thin slab castingprocess; heating to a rolling temperature of 1050 to 1250° C. or in-linerolling out of the casting heat; hot rolling the pre-strip or the slabor the thin slab to form a hot strip having a thickness of 12 to 0.8 mm,at a final rolling temperature of 1050 to 800° C.; reeling the hot stripat a temperature of more than 200 to 800° C.; pickling the hot strip;annealing the hot strip in a continuous or discontinuous annealinginstallation for an annealing time of 1 min to 48 h and at a temperatureof 540 to 840° C.; and cold rolling the hot strip at room temperature orelevated temperature in one or a plurality of rolling passes.
 20. Themethod of claim 19, further comprising adding to the steel melt byalloying at least one element in wt. % selected from the groupconsisting of Si: 0.05 to 0.7; Cr: 0.1 to 3; Mo: 0.01 to 0.9; Ti: 0.005to 0.3; B: 0.0005 to 0.01.
 21. The method of claim 19, furthercomprising subjecting the steel melt in blast furnace process orelectric arc furnace process to a vacuum treatment.
 22. The method ofclaim 19, further comprising electrolytically galvanising or hot-dipgalvanising the steel strip or applying another organic or inorganiccoating.
 23. The method of claim 19, wherein the hot strip is coldrolled at a temperature of 60 to 450° C.
 24. The method of claim 19,wherein during cold rolling in a plurality of rolling passes the hotstrip is selectively intermediately heated or cooled to a temperature of60 to 450° C. between the rolling passes.
 25. The method of claim 19,further comprising, after cold rolling at room temperature or elevatedtemperature, annealing the steel strip in a continuous annealinginstallation for an annealing time of 1 to 15 min and at a temperatureof 720° C. to 840° C., or by a discontinuous annealing installation foran annealing time of 30 min to 48 h and at a temperature of 550° C. to820° C.
 26. The method of claim 19, further comprising, after undergoingannealing, cooling the steel strip to a temperature of below 250° C. toroom temperature, subsequently reheating the steel strip to atemperature of 300 to 450° C., maintaining the steel strip at thetemperature of 300 to 450° C. for up to 5 min, and subsequently coolingthe steel strip to room temperature.
 27. The method of claim 19, furthercomprising temper-rolling the steel strip after cold rolling.
 28. Themethod of claim 22, further comprising applying a further coating on anorganic or inorganic basis upon the steel strip after electrolyticgalvanising or hot-dip galvanising.
 29. The method of claim 19, furthercomprising cold forming or warm forming the steel strip into astructural component.
 30. The method of claim 29, wherein warm formingof the steel strip is executed at a temperature of 60 to 450° C.
 31. Aultra high strength steel strip having a TRIP/TWIP effect, said steelstrip comprising: an alloy composition containing (in wt. %): C: 0.1 to<0.3; Mn: 4 to <8; Al: >1 to 2.9; P: <0.05; S: <0.05; N: <0.02; with theremainder being iron including unavoidable steel-associated elements;and a microstructure (in vol. %) including as phase components 10 to 80%austenite, 10 to 90% martensite, with the remainder being ferrite andbainite having a proportion together of less than 20%.
 32. The steelstrip of claim 31, further comprising at least one element in wt. %selected from the group consisting of Si: 0.05 to 0.7; Cr: 0.1 to 3; Mo:0.01 to 0.9; Ti: 0.005 to 0.3; B: 0.0005 to 0.01.
 33. The steel strip ofclaim 31, wherein a sum of the contents of Mn and Al (in wt. %)satisfies a following requirement: 6.5<Mn+Al<10.
 34. The steel strip ofclaim 31, wherein a proportion of at least 20% of the martensite ispresent as annealed martensite.
 35. The steel strip of claim 31, whereina proportion of >10% of the austenite is present in the form ofannealing or deformation twins.
 36. The steel strip of claim 31, havingan average grain size of the phase components: austenite: less than 500nm, martensite, ferrite, bainite: less than 650 nm.
 37. The steel stripof claim 31, having a tensile strength Rm of 1100 to 2200 MPa, a 0.2%elasticity limit Rp0.2 of 300 to 1550 MPa, and an elongation at fractureA80 of more than 4 to 41%.
 38. The steel strip of claim 31, wherein thesteel strip is defined by the following dependencies of tensile strengthRm in MPa and elongation at fracture A80 in %: Rm of over 1100 to 1200MPa: Rm×A80≥25000 up to 45000 MPa % Rm of over 1200 to 1400 MPa:Rm×A80≥20000 up to 42000 MPa % Rm of over 1400 to 1800 MPa: Rm×A80≥10000up to 40000 MPa % Rm of over 1800 MPa: Rm×A80≥7200 up to 20000 MPa %.39. The steel strip of claim 31, further comprising a galvanisation coatformed by galvanising the steel strip, and a further metallic, Inorganicor organic coating on the galvanisation coat.
 40. The steel strip ofclaim 31, produced by a method comprising: melting a steel meltcontaining (in wt. %): C: 0.1 to <0.3; Mn: 4 to <8; Al: >1 to 2.9; P:<0.05; S: <0.05; N: <0.02; with the remainder being iron includingunavoidable steel-associated elements, in a blast furnace process orelectric arc furnace process with optional vacuum treatment of the melt,casting the steel melt to form a pre-strip by a horizontal or verticalstrip casting process approximating a final dimension or casting thesteel melt to form a slab or thin slab by a horizontal or vertical slabor thin slab casting process, heating to a rolling temperature of 1050to 1250° C. or In-line rolling out of the casting heat, hot rolling thepre-strip or the slab or the thin slab to form a hot strip having athickness of 12 to 0.8 mm, at a final rolling temperature of 1050 to800° C., reeling the hot strip at a temperature of more than 200 to 800°C., pickling the hot strip, annealing the hot strip in a continuous ordiscontinuous annealing installation for an annealing time of 1 min to48 h and at a temperature of 540 to 840° C., and cold rolling the hotstrip at room temperature or elevated temperature in one or a pluralityof rolling passes.